5.5 Metamorphic Rocks

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Vocabulary

foliated: The thin flat layer which can be found in a metamorphic rock. Foliated means leaf in Latin.

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Outline

How Metamorphic Rocks Form

• Deep beneath the Earth's surface, heat and pressure can change any rock into a metamorphic rocks
  • When a rock undergoes the changes to become a metamorphic rock, its appearance, texture, crystal structure and mineral content change as well
  • The rock goes down to the mantle when collisions between the Earth's crust force down rock
    • The deeper the rock goes, the greater the pressure on the rock
      • The rock which is under hundreds or thousands the times the pressure then on the surface can change the minerals in a rock

Classifying Metamorphic Rocks

• When the metamorphic rocks are forming, the pressure also occurs on the rock's grains
  • Tremendous pressure can cause the grains to line up in straight parallel lines
    • This is how geologists classify metamorphic rocks
  • The grains which are in parallel layers are said to be foliated
    • Foliated rocks split easily along the bands
      • Ex. shale
        • When shale is under heat and pressure, it transforms into slate
        • In the process, hornblende and mica form
  • Some metamorphic rocks are not foliated
    • Non-foliated rocks do not split at the bands
      • Marble and